Image processing method for post-discharge plasma wall inspection in tokamaks, with application to ITER

Periodic inspection of the ITER Plasma-Facing Components (PFCs) is essential to assess its condition under harsh plasma environments and disruptions, and to ensure reliable operation for subsequent plasma discharges. An inspection method planned for ITER involves a set of wide-angle visible cameras, with in-vessel components illuminated by wall-cleaning discharges. In order to test this approach, a dedicated experiment has been conducted at the Experimental Advanced Superconducting Tokamak (EAST). An Ion Cyclotron (IC) power-induced plasma glow is generated inside EAST, enabling image acquisition using a visible camera system. Images are captured under varying conditions of IC power, magnetic field, gas species, and pressure. While this method successfully produces a glow inside the tokamak, the plasma emission intensity can be either too high or too low, making it difficult to clearly resolve internal structures from individual raw camera images. To address this limitation, an enhancement-based post-processing algorithm is applied to images acquired using deuterium (D 2 ) and helium (He) plasmas under different operating conditions. The distribution used in the contrast-limited adaptive histogram (CLAHE) equalization step is selected empirically for each imaging condition. The effectiveness of the Rayleigh and exponential distributions depended on the gas species, IC power, exposure time, and recorded intensity distribution. The combination of controlled acquisition parameters and enhancement-based processing substantially improved the visual interpretation of IC-induced plasma-glow images, as further supported by intensity-profile analysis. The proposed method provides a post-processing tool for investigating the visibility of plasma-facing components in tokamak environments. Validation under ITER-specific imaging and operating conditions remains necessary.